Assisted and/or artificial ventilation systems are an essential component of modem medicine. Generally, such systems provide inspiratory fresh gases to a patient from a source of same, such as from an anesthesia or a ventilator machine, and conduct expired gases away from the patient. Inspiratory gases are conducted through a different conduit from the expired gases and thus at least two conduits are required. Commonly used circuits have two limbs (e.g., two independent tubes). The ends of the tubes in a breathing circuit are generally held in spaced relationship by a connector located at the patient, or distal, end of the circuit. The connector can place the distal (i.e., patient) ends of the tubes in a fixed parallel relationship, or the connector can be a Y-piece with the two tubes converging at an angle. Conventional respiratory tubes are corrugated and flexible to permit movement while minimizing collapse and kinking of the tubes. Recently, the use of axially expandable and contractible pleated (“accordion-like”) tubing has become popular. Commonly used accordion-like or pleated tubing is known as ULTRA-FLEX® (available from King Systems Corporation, Noblesville, Ind., U.S.A.), FLEXITUBE® or ISOFLEX™, in which the length can be adjusted by axially expanding or contracting one or more pleats between a closed and open position. Whether the pleats are in the open or closed position, the tube wall remains corrugated to minimize the risk of kinking or collapse upon convolution or bending of the tubing.
Respiratory Care and ICU Type Non-Rebreathing System
In a non-rebreathing breathing system, which can be used for respiratory care or in an intensive care unit (ICU), a one-way valve permits gases to flow to a patient through an inspiratory conduit, while another one-way valve causes expired gas from the patient to flow through an expiratory conduit and then to an exhaust conduit.
Circle CO2 Absorption and Mapleson Type Breathing Systems
In a “circle system,” a one-way valve permits gas to flow to a patient through a first or inspiratory conduit, while another one-way valve permits partial recirculation of the gases by causing expired gases to flow from the patient through a second or expiratory conduit to a “recirculation module” or “scrubber circuit”, which generally comprises a carbon dioxide absorber to eliminate the expired carbon dioxide resulting in “scrubbed gases”. The scrubbed gases are then combined with the fresh gases coming from the anesthesia machine, and the mixed gases are referred to herein as “refreshed gases”. Some or all of the refreshed gases can be rebreathed by the patient. Excess gases are directed to an exhaust conduit and/or scavenger. Thus, new fresh gases are combined with scrubbed gases at the scrubber circuit, and are delivered as refreshed gases to the first conduit, while expired gases are carried by a second conduit to a “scrubber circuit” for re-circulation and/or exhaust.
It is believed that in low flow anesthesia with the circle system, the anesthetic concentration of the refreshed gases decreases progressively from the initial fresh gas concentration (concentration at the vaporizer) in the process of recirculation. Such a decrease may be due to dilution by the expired gases and/or scrubbed gases, leakage, and adsorption and/or absorption by plastic, rubber and other materials in the system. Therefore, low flow anesthesia, including totally closed anesthesia using prior art circle systems, is in theory possible, but very limited in practice.
In Mapleson A-F type circuits, fresh gas is delivered into a common breathing tube by a fresh gas delivery/supply tube, wherein the breathing tube acts to provide gases to the patient and receive expired gases therefrom. Generally, the diameter of the fresh gas supply tube is small thereby limiting its function to being a fresh gas delivery or supply conduit rather than an inspiratory tube (i.e., a tube from which a patient directly inspires as in a circle system). A Mapleson D type circuit (the most commonly used circuit among the Mapleson circuits) does not use valves, therefore, the flow of fresh gases required is sufficiently high to minimize CO2 rebreathing. During inspiration, the patient will inhale fresh gases from the fresh gas delivery/supply tube inlet and gases from the common breathing tube, which may be a mixture of fresh gas and expired alveolar gases. High fresh gas flow will flush the breathing tube, pushing the expired alveolar gases out of the circuit.
The Bain Circuit
An embodiment of a unilimb modification of the Mapleson D type circuit, often referred to as a “Bain circuit” or “Bain,” is described in U.S. Pat. No. 3,856,051, in which the fresh gas delivery line is inserted through the wall of the common breathing tube near the proximal rather than near the distal end thereof, and the delivery tube then extends lengthwise through the common breathing tube so that its distal end is near the distal end of the common breathing tube. This creates a unilimb circuit from dual members. The fresh gas delivery line is sealably bonded to the common breathing tube at its junction therewith.
Another embodiment of a Mapleson D type circuit is described in U.S. Pat. No. 5,121,746, to Sikora, in which a flexible corrugated tube is divided by an internal common wall into a larger and smaller flow passage and is provided with a bayonet type connector at the patient end and a double friction fit connector at the machine end. A modification of the circuit described in this patent is used to form a circle circuit sold as the Limbθ™ by Vital Signs, Inc. of Totowa, N.J., USA.
The Universal F® Circuit
With reference to U.S. Pat. No. 4,265,235, to Fukunaga, a unilimb device of universal application for use in different types of breathing systems is described which provides many advantages over prior systems. The Fukunaga device, sold as the Universal F® by King Systems Corporation of Noblesville, Ind., U.S.A., utilizes a space saving co-axial, or tube within a tube, design to provide inspiratory gases and remove expiratory gases. Numerous advantages flow from this arrangement, such as a reduction in the size of the breathing apparatus connected to a patient. Further, the device acts as an artificial nose since the expired gases warm and maintain humidity of the inspired gases as the two opposing flows are countercurrent in the unilimb device.
Universal F2® Technology
With reference to U.S. Pat. No. 5,778,872, to Fukunaga et al., unilimb multi-lumen circuits are disclosed and embodiments thereof are sold as the F2™ or Universal F2® by King Systems Corporation of Noblesville, Ind., U.S.A., which have revolutionized artificial ventilation systems and methods of providing assisted ventilation and anesthesia. The F2™ system provides for safe and ready attachment and detachment of multilumen (e.g., co-axial) system components from the proximal terminal. This permits more efficient placement and utilization of other breathing circuit components, improves system performance, and yet reduces medical waste and costs. In general, the Universal F® and the F2™ are used in a circle system configuration with a carbon dioxide absorber. For more information about the F2™ technology, one may contact King Systems Corporation.
For further information on breathing systems, and anesthetic and assisted ventilation techniques, see U.S. Pat. Nos. 3,556,097, 4,007,737, 4,188,946, 4,265,235, 4,463,755, 4,232,667, 5,284,160, 5,778,872, Austrian Patent No. 93,941, British Patent 1,270,946, Dorsch, J. A., and Dorsch, S. E., Understanding Anesthesia Equipment: Construction, Care And Complications Williams & Wilkins Co., Baltimore (1974), and Andrews, J. J., “Inhaled Anesthetic Delivery Systems,” in Anesthesia, 4th Ed. Miller, Ronald, M. D., Editor, Churchill Livingstone, Inc., N.Y. (1986). The text of all documents referenced herein, including documents referenced within referenced documents, is hereby incorporated by reference as if same were reproduced in full below.
Cost Effective Anesthesia Systems and Unconventional New Era Respiratory Conduits
Hospitals, medical personnel, and related entities are always looking for ways to improve medical care. Numerous monitoring standards have been implemented to ensure that the required medical care is being safely administered. For example, in the field of respiratory care and anesthesia, non-invasive and invasive monitoring methods have become routinely used, such as alarm monitoring systems that warn the user of obstruction and/or disconnection of gas flows, inspired and end-tidal gas monitoring, oxygen saturation monitoring by pulse oximeter, arterial blood gas and mixed venous blood gas monitoring. These techniques and devices enable continuous patient monitoring, which permits the vigilant healthcare practitioner to more accurately adjust or titrate the necessary dosages of anesthetic gases or drugs, and readily detect problems due to the pathophysiologic condition of the patient or due to those caused by medical equipment failure or settings. There is a desire for an anesthesia system that can optimize the use of such expensive monitoring equipment, which for example, could be used to decrease the waste of anesthetic gases.
Respiratory care is commonly and increasingly provided in medicine. Respiratory care includes, for example, artificial ventilation techniques, such as assisted ventilation and/or oxygen therapy. Certain devices widely used in respiratory care include breathing circuits, filters, HME's (heat and moisture exchangers), endotracheal tubes, laryngeal masks, laryngeal tubes, and breathing masks. Breathing circuits comprised of rigid pipes or flexible corrugated tubes made of rubber, plastic or silicon flexible tubes have been widely used all over the world for almost a century. In order to prevent cross contamination, “single use” breathing circuits are disposed of after a single use, or alternatively, more sturdy and more expensive reusable breathing circuit are used that can be sterilized by autoclave or other means. Both types of circuits are expensive to produce and/or use. Sterilization of the circuit requires substantial labor and processing costs, likewise disposing of the breathing circuit after a single use, while it is very effective in preventing cross contamination, also results in additional cost to the hospital.
U.S. Pat. No. 5,901,705, to Leagre, discloses a sleeve and filter for a breathing circuit, wherein the filter and a tubular sleeve or sheath encase a breathing circuit during use. The filter housing has two ports, one port is for connection to a patient and the other to the distal end of a breathing circuit. The sleeve is connected to the exterior of the filter housing and is extendable in a proximal direction over the breathing circuit. After use, the filter and sleeve are discarded, while the breathing circuit is reused for multiple patients. The sleeve and filter reduces the need for sterilizing the circuit after each use. The sleeve is constructed of a lightweight, relatively inexpensive material to help minimize the costs of producing the sleeve member. A clear, extruded polyethylene, polypropylene or polyvinyl film having a thickness generally similar to a heavy-duty plastic food storage bag has been found to perform admirably in this role as a sleeve member. The sleeve does not serve as a conduit for providing or exhausting respiratory gases.
U.S. Pat. No. 5,377,670, to Smith, discloses a casing or envelope for a breathing circuit to reduce heat transfer between the corrugated tube and the ambient atmosphere, thus the case or sleeve of the breathing circuit serves as an insulation means. The envelope or casing is not a conduit for providing inhaled and receiving exhaled gases. U.S. Pat. No. 5,983,896, to Fukunaga, discloses a multilumen unilimb breathing circuit that provides the advantages of maintaining humidity and temperature due to the counter-current effect of the gases.
While the above devices fulfill their respective, particular objectives and requirements, the aforementioned patents and the prior art do not describe a device wherein at least one of the respiratory conduits is comprised of a non-conventional (also referred to as “new era”) pipe or tube (i.e., different from a rigid-walled tube, pipe, corrugated tube, or pleated tube), which is both axially and radially flexible, but which has little or no compliance beyond a certain conduit radius and/or volume. By radially flexible, it is meant that the diameter of the conduit can be substantially reduced or the conduit can be relaxed or collapsed in cross-section in comparison to rigid-walled conventional tubing. This is distinguished from axially bending the tubing without substantially altering the cross-sectional area of the tube at the bend as is possible with rigid-walled prior art tubing. Prior art rigid-walled respiratory conduits maintain patency under ambient conditions as well as under the pressure differentials between their interior and exterior that occur during use for providing inspiratory and/or receiving expiratory gases. Since these prior art respiratory conduits do not radially collapse under ambient conditions (e.g., when not in use), they require greater space for shipping and storage, and they require thicker walls to have sufficient rigidity to avoid collapse under ambient and operating conditions. Thus, a greater amount of plastic is used to produce such tubing, which increases costs, as well as the volume of the waste produced.
In general, circuit compliance (i.e., expansion of the volume of circuit tubing under operating pressures) is undesired as it interferes with the accuracy and precision of gas administration. Further, excessive compliance may lead to insufficient gases reaching the patient's lungs.
The present inventors discovered that, so long as the respiratory conduits, and preferably the inspiratory conduit, can maintain patency for inspiratory and expiratory gases, the conduits do not need to be always patent like rigid-walled pipes or tubes (e.g., corrugated plastic tubes that maintain a fixed diameter at ambient conditions and/or which are relatively rigid or straight). The respiratory conduits of the present invention should, however, provide low resistance and little compliance during use sufficient to meet the requirements for spontaneous and assisted ventilation. It is preferred that the inspiratory conduit permit gas flow at all times, and even under negative pressure, and that the expiratory line provide positive pressure even in spontaneous ventilation.
Definitions
To facilitate further description of the prior art and the present invention, some terms are defined immediately below, as well as elsewhere in the specification. As used herein, the term “artificial or assisted ventilation” shall also incorporate “controlled and spontaneous ventilation” in both acute and chronic environments, including during anesthesia. Fresh gases include gases such as oxygen and anesthetic agents such as nitrous oxide, halothane, enflurane, isoflurane, desflurane, sevoflurane, that are generally provided by a flowmeter and vaporizer. The end of a conduit directed toward a patient shall be referred to as the distal end, and the end of a conduit facing or connected to a source of inspiratory gases shall be referred to as the proximal end. Likewise, fittings and terminals or other devices at the distal end of the breathing circuit, e.g., connecting to or directed at the patient airway device (i.e., endotracheal tube, laryngeal mask, laryngeal tube, face mask etc.), will be referred to as distal fittings and terminals, and fittings and terminals or other devices at the proximal end of the breathing circuit will be referred to as proximal fittings and terminals. So, a distal adaptor or connector would be located at the distal or patient end of a circuit.
It is generally understood that a proximal terminal in a multilumen unilimb breathing circuit context is located at the machine end of the circuit and separates at least two independent flow paths that are in parallel closely-spaced or apposed relationship or that are coaxial in the circuit so that at least one flow path can be connected to a source of inspiratory gases while another flow path can be connected to an exhaust port that is spaced from the inspiratory gas port. A proximal terminal may also comprise a rigid housing that merges two independent flow paths into a common flow path, for example a Y-type fitting, preferably with a septum. The use of a proximal fitting with a proximal terminal in a unilimb circuit is a new concept brought about by the Universal F2® inventions, which for the first time made it possible to readily connect and disconnect plural tubes to a proximal terminal on an assisted ventilation machine via a corresponding proximal fitting. Unlike the proximal terminal, when a proximal fitting comprises multiple lumens, the proximal fitting maintains the spatial relationship of the proximal ends of the tubes forming a multilumen circuit. Hence a proximal fitting in a breathing circuit is to generally be understood as a fitting which permits ready connection of tubing to a proximal terminal which can provide inspiratory gases and exhaust expiratory gases from separate spaced ports. In some embodiments of the present invention tubing may be directly bonded to a proximal terminal, while in other embodiments tubing may connect to a proximal fitting that can engage a corresponding port or ports on a proximal terminal. The proximal fitting may include filter means, or may engage a filter which in turn connects to a proximal terminal.
The term conduit broadly comprises fluid carrying members without being limited to conventionally used corrugated tubes, such as those used in presently available breathing and/or anesthesia circuits (i.e., a conduit has a lumen defined by one or more walls, has a variety of shapes and diameters, and serves the purpose of carrying inspiratory gases to or expiratory gases from a patient). For example, conduits for use with the present inventions may comprise flexible fabric or plastic sheaths (like a film or sheet made of plastic, such as polyvinyl, that can have a cylindrical or tubular form when gases or fluid are contained, but collapses or looses the tubular form when deflated or emptied) and/or flexible tubes that may be smooth-walled, straight, corrugated, collapsible, and/or coiled. In this respect, certain embodiments of the present invention substantially depart from the conventional concept and design of prior art respiratory conduits. Embodiments of flexible conduits for carrying respiratory gases to and/or from a patient in accordance with the present invention can be both flexible in the radial and axial directions up to a maximum volume and/or radius (or maximum cross-sectional area where the cross-sectional shape is not circular), and have a wide variety of cross-sectional shapes, and in so doing provide a low cost apparatus very well suited to providing respiratory care, i.e., assisted ventilation to a patient, which is effective and practical.
Unconventional or non-conventional tubular conduits refer to conduits used in a respiratory circuit for carrying patient inspiratory and/or expiratory gases that are made of materials and/or have shapes not previously used in assisted ventilation or anesthesia machines for carrying inspiratory and expiratory gases between a patient or other mammal and the machine. By carrying patient inspiratory and/or expiratory gases, it is understood that the gases are being provided via a conduit to a patient from a source (e.g., ventilator machine) and exhausted via the same and/or another conduit to an exhaust (e.g., assisted ventilation machine). For example, a coiled inspiratory or expiratory conduit when used in accordance with the present invention is a non-conventional tubular conduit. Likewise, a conduit formed of flexible, gas impermeable fabric, such as but not limited to extruded polyethylene, polypropylene or polyvinyl film, that is radially expandable to a maximum radius and volume under pressures generally used in assisted respiration and is collapsible when the pressure inside of same is less than ambient pressure or the pressures generally used in assisted respiration, can be used as a non-conventional respiratory conduit in accordance with the present invention. Ambient pressure refers to the pressure normally encountered outside of tubes, which is generally atmospheric pressure. Such conduits can maintain patency as needed in use yet readily relax or collapse (collapsing may require some assistance depending on the embodiment) to smaller diameters, lengths, and volumes, particularly when the internal pressure inside is sufficiently lower than the pressure outside of the conduit.
For the purposes of brevity, the term Suave™ flexible tube is used to describe a flexible respiratory conduit for use in carrying respiratory gases (i.e., gases to be inspired and expired gases to be exhausted) between a patient and a ventilation machine or respiratory care device in which the conduit is radially collapsible when not in use, and can expand to a maximum predetermined diameter (or maximum cross-sectional area; maximum diameter and maximum radius incorporate maximum cross-sectional area when the cross-sectional shape is not circular) and volume during use (such a conduit shall be hereinafter referred to in this document as a suave tube or suave conduit; no trademark rights are waived by use of the term suave or any other mark used herein regardless of case or inclusion of the ™ or ® symbol). Upon expansion to its maximum diameter (i.e., maximum cross-sectional area) a suave tube exhibits substantially the same compliance in assisted ventilation applications as conventional corrugated tubes or pleated tubing (i.e., ULTRA-FLEX®) conduits. Suave flexible tubes may also be axially expanded or contracted. Suave tubes are much less expensive to manufacture than conventional conduits having a relatively rigid diameter or cross-sectional shape, such as those formed of corrugated tubing.
Preferred radially collapsible tubes for use in the present invention will, when inflated at pressures encountered in providing assisted ventilation and/or anesthesia to humans and other mammals, have a compliance of less than about 50%, preferably less than about 20%, more preferably less than about 10%, even more preferably less than about 5%, and most preferably less than about 2%. Preferred radially collapsible tubes for use in the present invention have a minimum cross-sectional area when fully inflated sufficient to meet the desired flow characteristics (hereinafter, referred to as the inflated cross-sectional area), and can collapse so that the collapsed cross-sectional area is preferably less than about 90% of the inflated cross-sectional area, more preferably less than about 70% of the inflated cross-sectional area, even more preferably less than about 50% of the inflated cross-sectional area, even more preferably less than about 25% of the inflated cross-sectional area, and most preferably less than 10% of the inflated cross-sectional area.
In one embodiment, the suave tubes are shipped and stored in collapsed form, and after inflation thereof no subsequent effort may be made to collapse them, except optionally to compress the suave tubes to a smaller volume for disposal. In this way, manufacture, shipping and storage costs are minimized. Gravitational forces will cause the suave tubes to collapse to varying degrees in some embodiments when not pressurized sufficiently.
Breathing Circuit Requirements
A patient requiring artificial ventilation or anesthesia may be positioned in an awkward position and depending on the surgical site the required length of the circuit may vary. This is also so in patients undergoing diagnosis, e.g., MRI, CT scans, etc. It is therefore desirable to have a breathing circuit that is flexible and that the length of both the inspiratory or fresh gas delivery tube and the expiratory or exhaust tube can be adjusted while minimizing disconnections, obstructions, entangling and kinking. It is also desirable to have breathing circuits that are light in weight. Furthermore, for cost containment, the health care providers (i.e., hospital, physician, ambulatory surgery center, nursing homes, etc.) require inexpensive breathing circuits and/or inexpensive methods to provide artificial ventilation or anesthesia to patients in need thereof.
Breathing circuits may be classified based on how carbon dioxide is eliminated. Carbon dioxide can be eliminated by “washout”, which is dependent on the fresh gas inflow (i.e., CO2 absorption is not required, e.g., in a Mapleson type circuit), or by using a CO2 absorber such as soda lime and the like, (i.e., as in a circle circuit). Thus, breathing circuits in anesthesia are generally provided as circle circuits (CO2 absorption system) or Mapleson type circuits. Because Mapleson D type partial rebreathing systems require high fresh gas flows, the circle system is the most widely accepted system. Breathing systems wherein low fresh gas flow can be utilized are advantageous because of reduced consumption and waste of fresh gases (e.g., anesthetic gases), ecological benefits (reduced environmental pollution), and cost-savings. However, a major concern of low flow techniques in anesthesia is the efficiency of fresh gas utilization and the unpredictability concerning the alveolar or inspired concentration of anesthetics provided to the patient that should be administered in sufficient dosages to achieve desired anesthetic endpoints (e.g., avoid awareness during surgery without overdosing). Moreover, there is a significant discrepancy between the volatile anesthetic vaporizer setting concentration and the inspired concentration of anesthetic gases. A further concern with the circle system is the interaction of volatile anesthetics with the carbon dioxide absorber (e.g., soda lime), which has been recently reported as producing toxic substances. This concern includes the formation of carbon monoxide and Compound A during degradation of volatile anesthetics by soda lime. For example, CO has been found in anesthetics, including halothane, enflurane, isoflurane and desflurane circle systems. Moreover, in the case of sevoflurane, it is known that sevoflurane is degraded in the presence of soda lime to olefin and Compound A, which has been reported to have nephrotoxic potential at clinical concentrations. Further, it is desired to reduce waste of expensive anesthetic and respiratory gases in circle systems and Mapleson type systems.
A major concern with prior unilimb breathing circuits is that the inspiratory gas or fresh gas line not become disconnected or blocked (e.g., via kinking) during use. For this reason, rigidly bonding the proximal end of the inspiratory gas line to the fresh gas inlet fitting was stressed, while the distal end was permitted to move with respect to the distal end of the outer conduit (e.g., exhaust conduit), which could create a variable dead space. Despite the surprising discovery reported in U.S. Pat. No. 5,778,872, to Fukunaga, that an appropriate dead space in a breathing circuit could be beneficial by yielding normocapnia without hypoxia, there is still a desire for a circuit that has either a minimum and/or fixed dead space regardless of circuit manipulation, yet is flexible and safe. Further, there is a desire for systems that more efficiently utilize anesthetic gases in a safe and predictable manner. It is also desired that the same breathing circuit be utilized in both adult and pediatric cases, or at least in a greater number of patients, thereby minimizing the need for circuits of different size. There is also a need for breathing circuits and systems that are simpler, lightweight, cost-effective, safer, and/or easier to operate and handle than prior circuits and systems.